Visualising Varnish Removal for Conservation of Paintings by Fluorescence Lifetime Imaging (FLIM)

TY - JOUR

T1 - Visualising Varnish Removal for Conservation of Paintings by Fluorescence Lifetime Imaging (FLIM)

AU - Wilda, Christine

AU - Burnstock, Aviva

AU - Della Rocca, Francescopaolo Mattioli

AU - Henderson, Robert

AU - Nedbal, Jakub

AU - Suhling, Klaus

N1 - Funding Information: Funding was provided to King’s College by United Kingdom Research and Innovation (UKRI) (BBSRC Award Number: BB/R004803/1 and EPSRC award number: EP/R511559/1). The SPAD camera was developed with funding provided to The University of Edinburgh by UKRI (EPSRC award numbers: EP/M01326X/1 and EP/T00097X/1). Publisher Copyright: © 2023, The Author(s).

PY - 2023/6/16

Y1 - 2023/6/16

N2 - The removal of varnish from the surface is a key step in painting conservation. Varnish removal is traditionally monitored by examining the painting surface under ultraviolet illumination. We show here that by imaging the fluorescence lifetime instead, much better contrast, sensitivity, and specificity can be achieved. For this purpose, we developed a lightweight (4.8 kg) portable instrument for macroscopic fluorescence lifetime imaging (FLIM). It is based on a time-correlated single-photon avalanche diode (SPAD) camera to acquire the FLIM images and a pulsed 440 nm diode laser to excite the varnish fluorescence. A historical model painting was examined to demonstrate the capabilities of the system. We found that the FLIM images provided information on the distribution of the varnish on the painting surface with greater sensitivity, specificity, and contrast compared to the traditional ultraviolet illumination photography. The distribution of the varnish and other painting materials was assessed using FLIM during and after varnish removal with different solvent application methods. Monitoring of the varnish removal process between successive solvent applications by a swab revealed an evolving image contrast as a function of the cleaning progress. FLIM of dammar and mastic resin varnishes identified characteristic changes to their fluorescence lifetimes depending on their ageing conditions. Thus, FLIM has a potential to become a powerful and versatile tool to visualise varnish removal from paintings. Graphical Abstract: [Figure not available: see fulltext.]

AB - The removal of varnish from the surface is a key step in painting conservation. Varnish removal is traditionally monitored by examining the painting surface under ultraviolet illumination. We show here that by imaging the fluorescence lifetime instead, much better contrast, sensitivity, and specificity can be achieved. For this purpose, we developed a lightweight (4.8 kg) portable instrument for macroscopic fluorescence lifetime imaging (FLIM). It is based on a time-correlated single-photon avalanche diode (SPAD) camera to acquire the FLIM images and a pulsed 440 nm diode laser to excite the varnish fluorescence. A historical model painting was examined to demonstrate the capabilities of the system. We found that the FLIM images provided information on the distribution of the varnish on the painting surface with greater sensitivity, specificity, and contrast compared to the traditional ultraviolet illumination photography. The distribution of the varnish and other painting materials was assessed using FLIM during and after varnish removal with different solvent application methods. Monitoring of the varnish removal process between successive solvent applications by a swab revealed an evolving image contrast as a function of the cleaning progress. FLIM of dammar and mastic resin varnishes identified characteristic changes to their fluorescence lifetimes depending on their ageing conditions. Thus, FLIM has a potential to become a powerful and versatile tool to visualise varnish removal from paintings. Graphical Abstract: [Figure not available: see fulltext.]

UR - https://doi.org/10.18742/c.6137130

UR - http://www.scopus.com/inward/record.url?scp=85162038337&partnerID=8YFLogxK

U2 - 10.1186/s40494-023-00957-w

DO - 10.1186/s40494-023-00957-w

M3 - Article

SN - 2050-7445

VL - 11

JO - Heritage Science

JF - Heritage Science

IS - 1

M1 - 127

ER -